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i.thomson
United Kingdom
408 Posts |
 Posted - 16/02/2014 : 12:00:36
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You're right Chris but it's only really a convention. Sticking to this method ensures that the fuse still operates to protect the wiring on circuits which have only one accessible return lead. In these circumstances there is a shared return lead (it is only really a "ground" or "earth" lead when it is actually connected to the actual ground or earth) and although fusing it would provide protection it would also affect all other circuits which are using it as a return. It goes without saying that using the chassis as a return as in our cars that fusing this is rather impractical. Having said all that if you are fusing an individual circuit, as you are, with access to both leads, then the fuse will operate satisfactorily in either lead. This is similar to the perennial "problem" which people cite when connecting negative earth devices to positive earth cars. In this case simply making sure that the case is insulated from all other electrical connections (such as happens on a wooden dashboard), and connecting + and - to it correctly, it will work OK. I hope I haven't muddied the waters too much by including that.
Ian Thomson |
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MG Maverick
United Kingdom
1045 Posts |
Posted - 16/02/2014 : 12:10:41
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Thanks Ian,
Very clear and understood.
Chris ( J2353 )
Brighton, East Sussex & Paphos, Cyprus. |
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geoffw
Australia
106 Posts |
Posted - 17/02/2014 : 01:43:33
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Before I retired I was an Electrical Engineer & designed a number of charging systems for forklift battery installations.
Hydrogen discharging will not be a problem with 'battery conditioners' associated with our types of cars.
Hydrogen discharge during lead acid battery charging is dependant upon the rate of charge & the number of cells being charged (6 in the case of a 12V battery). The maximum rate of discharge is approx. 0.46 litres / ampere / cell / hour. My own unit has a charge rate of 0.75A, therefore the max. amount of hydrogen / hour is 0.46 x 0.75 x 6 or 2.07 litres/hour.
As even a small single car garage has a volume of 18,000l this represents .012% by volume. Hydrogen is flammable when the volume is in the range 4% to 90%.
Natural leakage in a well constructed garage is equal to 1 air change an hour so there is a safety factor in the order of 33 to 1.
Sorry about all the maths, it is just the Engineer in Me!! |
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Malcolm Eades
United Kingdom
379 Posts |
Posted - 17/02/2014 : 13:15:22
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Thanks Geoff. Don't apologise. It's good to have these things put into perspective by someone who knows the underlying science.
Malcolm
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